The present invention relates to cyclic phosphorus compounds, such as cyclic hydrogenphosphonates, processes for the preparation of such compounds and their derivatives, and to flame retardant compositions containing the said cyclic phosphorus compounds.
Certain phosphonates have been employed as flame retardant additives, but have suffered from the defect of causing undesirable crosslinking of polymeric materials in which the phosphonates were employed. For example, the addition of such phosphonates to a molten polymer such as polyethylene terephthalate or a nylon, preliminary to the extrusion or spinning step has shown that the crosslinking prevents the formation of acceptable fibers. As a result of the crosslinking, the fibers contain lumps and irregular sections so that the extrusion through spinnerettes is hampered and the stretching, washing and other physical treatments of the fiber become impossible.
It has now however been found that certain cyclic phosphorus compounds including cyclic phosphonates are particularly useful as flame retardants for organic polymeric materials. The invention includes combinations of the present cyclic phosphorus compounds together with organic polymers such as polyurethanes, polyesters, e.g. polyethylene terephthalate, and polyamides e.g., the nylons.